1. Field of the Art
The present invention relates to polymerization of olefins. Particularly, the present invention relates to a novel catalyst composition and a process for preparing an olefin with the use of the catalyst. More particularly, the present invention relates to a process for polymerizing an olefin in which an olefin polymer having excellent particle properties can be prepared when the slurry polymerization method or the vapor phase polymerization method, particularly the vapor phase polymerization method, is employed, and in which an olefin copolymer having a narrow molecular weight distribution and a narrow composition distribution can be prepared with an excellent polymerization activity, and further in which a polymer which will produce a film product having an excellent appearance can be produced.
2. Background Art
Processes for preparing an ethylene-.alpha.-olefin copolymer with catalysts comprising a zirconium compound and an alumoxane as a novel Ziegler type catalyst are disclosed in, for example, Japanese Patent Laid-Open Publication Nos. 19309/1983, 35006/1985, 35007/1985, 35008/1985, 130604/1985, and 260602/1985.
The catalysts formed with the transition metal compound and the alumoxane as proposed in the prior techniques, notwithstanding their extensively excellent polymerization activities as compared with conventional Ziegler catalyst systems comprising a transition metal compound and an organoaluminum compound, were accompanied by certain problems. For example, the nature of the catalysts such that most of the catalyst systems proposed in the prior art are soluble in the polymerization system may favor their use in solution polymerization whereby not only there may be substantially no polymerization methods other than a solution polymerization method, but also the polymer solutions which are usual forms of a polymer produced in the solution polymerization have excessively high viscosity where the polymer has a high molecular weight. Moreover, the polymers obtained from the solution had only a low bulk density, so that it was also difficult to obtain a polymer having good particle properties.
Trials for polymerizing olefins by a suspension polymerization method or a vapor/gas phase polymerization method in the presence of a catalyst having one or both of the components of the transition metal compound and the alumoxane described above supported on a porous inorganic oxide carrier such as silica, silica-alumina or alumina have been performed. For example, it has been described in Japanese Patent Laid-Open Publication Nos. 35006/1985, 35007/1985 and 35008/1985 that the transition metal and the alumoxane supported on a carrier such as silica, silica-alumina or alumina can be used as a solid catalyst.
Additionally, Japanese Patent Laid-Open Publication Nos. 106808/1985 and 106809/1985 disclose a method for preparing a composition comprising a polyethylene polymer and a filler by copolymerizing ethylene or ethylene and an .alpha.-olefin in the presence of a product which has been obtained by the preliminary contact of an active catalyst comprising a hydrocarbon-soluble titanium and/or zirconium compound with a filler, and an organoaluminum compound as well as an additional filler which has an affinity for a polyolefin.
Further, a method of copolymerizing ethylene or ethylene and an .alpha.-olefin in the presence of a catalyst mixture comprising a product obtained by reacting a trialkylaluminum and water in the presence of silicon dioxide and aluminum oxide and a transition metal compound has been described in Japanese Patent Laid-Open Publication No. 31404/1986.
Japanese Laid-Open Publication No. 276805/1986 discloses a method of polymerizing an olefin in the presence of a catalyst comprising a zirconium compound and a reaction mixture of an alumoxane with a trialkylaluminum which are further reacted with an inorganic oxide having hydroxyl groups on the surface of the inorganic oxide such as silica.
Furthermore, a method of polymerizing an olefin in the presence of a catalyst having a transition metal compound such as a metallocene and an alumoxane supported on a carrier such as an inorganic oxide has been described in Japanese Laid-Open Publication Nos. 108610/1986 and 296008/1986.
To the best of our knowledge, the use of such catalysts comprising a transition metal compound and an alumoxane supported on a carrier as those disclosed produce polymers having lower granulometric properties such as a lower bulk density in a lower yield when the catalysts are used in a suspension or a gas phase polymerization than when they are used in a solution polymerization method. Additionally, these inorganic compounds used as the carrier remain in the polymers produced often to impair the physical properties or appearances of film products produced therefrom.
It has been described in Japanese Patent Laid-Open Publication Nos. 280703/1988 and 11604/1992 that polymers having a polymerization activity and a good particle property can be obtained even with only a small amount of an alumoxane when use is made of a transition metal component which has undergone a preliminary polymerization in the presence of a carrier/support material which has been treated with an organometallic compound. In this case, however, a coarse carrier could have often caused a problem of impairing the appearance of film products.
The conventional techniques had problems to be solved as described above and thus were hardly regarded as being fully satisfactory.